This application claims the priority of German Patent Application No. DE 101 41 969.9 filed Aug. 24, 2001, which is incorporated herein by reference.
This application is related to concurrently filed U.S. patent application No. 10/227,451 corresponding to German Patent application No. DE 101 41 570.0, filed Aug. 24, 2001, which is incorporated herein by reference.
The invention relates to a casing cover for an internal-combustion engine, particularly valve covers or oil pans to be mounted detachably and fluid-tight to an engine block, with an elastomer seal profile at the edge of the casing cover.
In engines, especially internal-combustion engines, it is unavoidable that a component, such as the engine block, will vibrate during engine operation. These vibrations may lead to an unpleasant noise level. A common measure for preventing the component vibrations from being transmitted to the parts adjoining the vibrating component, or only allowing them to be transmitted in damped form, is to integrate elastomer seal profiles into the adjoining parts, which assure an acoustic decoupling of the adjoining parts. This measure can often greatly reduce the noise level. The parts mounted to the component primarily include casing covers, such as valve covers or oil sump covers, i.e., oil pans, in internal-combustion engines. In this acoustic decoupling of the casing cover, a profiled elastomer seal is positioned between the casing cover and the engine block. The surface of the engine block on which the seal profile rests is referred to as the sealing surface.
A drawback of this use of elastomers is that they are prone to a more or less significant amount of relaxation. The relaxation is counteracted with, among other measures, combined decoupling devices.
By way of example, U.S. Pat. No. 5,255,647 proposes a vibration-decoupling device for a casing cover, in which, in addition to a screw decoupling, a decoupling element is disposed as a seal profile in the cover edge. In this case, the seal profile serves in sealing a space inside the casing cover, as well as in vibration-related decoupling between the casing cover and the engine block, while the screw decoupling serves to counteract the seal relaxation and the associated risk of leakage.
If such casing covers are produced from plastic, the generally low rigidity of plastic as compared to metal gives rise to the risk of displacement, that is, drifting as a result of relaxation or deformation of the edge of the casing cover between the fastening screws. Of course, it is also possible for metal casing covers to be displaced. While the screw decoupling counteracts a relaxation of the seal profile, it offers no assurance that the cover edge will not be displaced across the sealing surface.
For counteracting the relaxation of the seal profile, European published patent application No. EP 0 664 388 A1 proposes a generic casing cover as a valve cover for a cylinder head of an internal-combustion engine, in which the pre-stressing force on the seal can be adjusted with the use of a metallic spring body. In this instance, the seal profile at the cover edge is pressed against the engine block with a specific force during the tightening process. With the use of the metallic spring body, the valve cover is in a position to follow the relaxation of the seal profile.
A disadvantage of this casing-cover design is that, while the force on the seal can be maintained at a relatively constant level, there is no provision for preventing a shifting movement of the cover edges across the sealing surface. Shifting fatigue of the casing-cover material, for example, or excessive tightening moments of the cover screws. This is particularly the case when the casing-cover materials are insufficiently stable, the components cannot be constructed to be adequately rigid, or the screw arrangement is unfavorable.
The seal may be damaged by the shifting movement, or the sealing forces on the elastomer seal material may no longer suffice to prevent leaks.
It is therefore the object of the present invention to provide a casing cover that counteracts the shifting movements of the cover casing, and is provided with an acoustic decoupling mechanism.
The above object generally is achieved according to the present invention by a casing cover for an internal-combustion engine, particularly a valve cover or an oil pan, to be mounted detachably and fluid-tight to an engine block, with the cover having: a peripheral edge that is profiled to receive an elastomer seal and has an edge surface for engaging a sealing surface of an engine block; an axial extension disposed at an inner portion of the edge surface of the ceasing cover and oriented in the direction of an engine block, with the extension projecting axially beyond the edge surface of the casing cover and positioned so that the extension will extend beyond the sealing surface on the engine block when installed and at least correctly position the casing cover on an engine block; and a seal provided at least on an outer surface of the extension so as to provide a seal between the axial extension and the engine block when the cover is installed on an engine block. Advantageous modifications of the invention likewise are provided and discussed.
The concept underlying the invention overcomes the above-described technical drawbacks by providing an axial extension on the inside of the edge of the casing cover, with the extension being oriented in the direction of the engine block and projecting axially beyond the sealing surface when the casing cover is installed on the engine block, and at least one seal is disposed between the axial extension and the engine block.
The axial extension of the casing cover in accordance with the invention effectively prevents shifting movements of the cover edge. Instead, it is possible to manipulate the position of the cover on the sealing surface of the engine block. This purposeful positioning offers the advantage that the sealing surface on the engine block can be adapted exactly to the shape of the elastomer seal-profile material. This leads in turn to material savings with respect to the sealing surface, which positively influences the engine weight,
A further advantage is that the extension of the casing cover permits a purposeful, defined introduction of force into the elastomer sealing material, so the occurring tensions can be calculated and adjusted more reliably.
In addition to these advantages, the extension of the casing cover serves as a joining aid in the assembly process, and aids in positioning the casing cover during the mounting process. If, in accordance with the invention, the extension is formed such that it fixedly clamps the casing cover during the joining process, this greatly facilitates overhead assembly, as may be employed for oil pans.
In a first embodiment, the extension is disposed around the entire peripheral edge of the cover. Depending on the application and structural conditions, the extension can also only be formed only along part of the cover peripheral edge. The advantage of the partial embodiment is a lower weight, while the all-around embodiment offers more reliable guidance.
The extension projects beyond the sealing surface, in the direction of the engine block, and, in accordance with the invention, is shaped to engage an undercut in the inner wall of the engine block.
According to the invention, partial and all-around undercut engaging shapes are both conceivable. In fact, any undercut shape is conceivable, provided that the casing cover is detachable and is formed to be detached without damaging the extension. For example, rounded areas at the ends of the extension facilitate the joining of the casing cover.
In a further embodiment of the invention, the undercut engaging portion of the extension is formed in the shape of a sloped portion. The slope begins at the inside of the casing cover and extends in the direction of the outside of the casing cover and toward the inner wall of the engine block. The undercut engaging shape in the form of a slope offers the advantage that, in the event that the cover edge is shifted, the casing cover is drawn in the direction of the sealing surface, which simultaneously increases the sealing force. This advantageous effect can be utilized to influence the relationship between the shifting movement and the buildup of sealing forces. The undercut engaging shape in the form of a slope further offers the option of exerting a pre-stress on the seal profiles of the casing cover, thereby effecting a very precise positioning in the joining phase, which can in turn be beneficial for automated mounting procedures.
The arrangement of a further eloped portion at the axial lower end of the extension of the cover edge, with the further sloped portion being oriented in the opposite direction of the first slope, centers the casing cover in the joining phase. This greatly facilitates the handling of the casing cover in automated assembly processes.
Depending on the established dimensional tolerance, an additional sealing function can be realized through the production of the extension of the cover edge. This would be of great advantage if, for example, the fastening screws were inadequately tightened, giving rise to the risk of leakage.
In accordance with the invention, a structural adaptation between the sealing surface on the engine block and the extension of the casing cover can also simplify the joining of the casing cover. Thus, it is conceivable to provide a chamfer on the engine block to allow the extension to latch into the engine block.
The casing cover can comprise arbitrary materials, but, in accordance with the invention, it is preferably produced from a plastic. The extension according to the invention avoids the relaxation occurring in plastics, and the associated shifting movements of the seals on thee sealing surface.
To prevent the extension from coming into direct contact with the engine block, a further seal is disposed on the outer surface of the extension between the axial extension and the engine block, or the existing seal profile is formed or extended across the sealing surface and up to the end of the axial extension. If a further seal is provided as a separate part, the seal can be secured either in a form-fit or a non-positive lockup. A form-fit would be, for example, a seal in the shape of a U, with the two legs being pushed past the axial lower end of the extension. The adjustment of the leg spacing allows the stability of the seal seat to be adjusted. In a non-positive lockup, it is conceivable to secure the seal to the outer surface of the extension using a vulcanizing or injection-molding method.
In a further embodiment of the invention, the seal profile is formed to extend across the sealing surface and up to the end of the axial extension. The advantage of this embodiment lies in the lower cost of the seal assembly. Form-fit and non-positive-lockup connections are also conceivable here.
The arrangement of a seal between the extension and the engine block prevents the casing cover from coming into contact with the engine block when vibrations occur during engine operation. The casing cover thus is acoustically decoupled.
Exemplary embodiments of casing covers are described in detail below in conjunction with drawings and the ensuing description.